Amazon has their own custom built 7 port usb 2.0 hubs with 5v/4a adapter for $19 shipped (prime). Ordered 7 for an antminer project, i'll report back how they work out.

http://www.amazon.com/gp/product/B00DQFGJR4/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=ATVPDKIKX0DER